Groundhog,
I have found that it is necessary in service businesses to be able to scale up or down your capacity when your business demand it.
If I run a business that sell labour, which most of us do, at say 100 hours a week on average then I need two full timers and one part timer. But what happens when someone goes out sick or is on holidays or a client rings and says the want an extra done.
The right way to set your self up for 100 hours imo is 5/ 6 part-timer, they will all want more hours so that when you need them they are likely to say yes and if you lose one then no big deal get another one.
This means that you have a pool of available resources that can stretch or shrink as the circumstances require. Instead of you working for the staff they are working for you.